Fiber optic devices use single or multiple strands or fibers each having an inner circular glass core coated with a circumferential cladding having a different index of refraction. Light is transmitted along the core and totally reflected from the interface between the core and cladding. Such devices can be used as transmission lines for transmitting information bearing light energy. A transmission line can be formed from a single fiber or it can include a plurality of fibers bundled together as a cable. Additionally, several transmission lines can be arranged in parallel for the simultaneous transmission of information along each of the separate lines.
Where the transmission line is relatively long and extends between different pieces of apparatus, the transmission line is broken down into segments and the different segments are connected to each other by use of separable fiber optic connectors which have been developed to meet this need. The principal design criteria of such connectors is to connect the transmission lines in an end-to-end relationship in such a manner as to minimize the loss of light energy as light traverses from one end of one line into the end of the adjacent segment of that line. The most efficient transfer of energy occurs when the axis of the two lines are in alignment. In other words, if the ends of the lines are out of alignment either due to a lateral displacement or to the fact that there is a slight angular displacement, light energy will be lost. Thus, most fiber optic connectors are designed to bring the ends of the transmission lines into as perfect an axial alignment as possible.
When a transmission line is made up of a plurality of individual fibers joined together to form a bundle or cable for the transmission of a single piece of information along the line, it is not critical or necessary that the individual fibers be aligned exactly with the ends of the fibers on the other cable since most of the light emitting from one end will be accepted into the fibers on the other side. However, where a transmission line is made up of a single individual fiber, it is more critical that the end of one be perfectly aligned with the end of the other to minimize energy loss. This problem becomes even more critical where there are several transmission lines connected in parallel to one another by means of the connector through which all of the lines pass. Due to differences in manufacturing tolerances, while one transmission line might be perfectly aligned, another one might be out of alignment. The state-of-the-art relevant to the invention is exemplified in the U.S. patents now to be discussed.
Three patents will now first be discussed as showing the state-of-the-art relative to connectors for transmission lines formed from cables or bundles of fibers.
U.S. Pat. No. 3,922,064--Clark et al discloses a "Self-aligning Optical Waveguide Connector" for a transmission line formed from a cable or bundle of fibers. The connector is for a single cable and includes provision of allowing both axial and lateral movement of the ends of at least one of the cable segments during the mating process. U.S. Pat. No. 3,999,837--Bowen et al discloses a "Light Transmitting Fiber Bundle Connector" one embodiment of which is designed to connect a single transmission line and the other embodiment (FIG. 12) connects a plurality of transmission lines in parallel. U.S. Pat. No. 3,982,815--Nakayama shows a "Connector For Light Transmitting Cables" in which a single transmission line is connected by means of a connector formed of identical parts. In one embodiment (FIG. 4), the ends of one transmission line is spring biased to allow for some axial movement during the mating process.
The art of connectors for single fibers or strands is exemplified by the following U.S. patents. U.S. Pat. No. 4,008,948--Dalgleish discloses "Optical Fibre Connectors" for either a single transmission line or plural parallel transmission lines. The ends of the individual lines are aligned in a specially shaped male member. U.S. Pat. No. 4,056,305--McCartney et al shows a "Single Optical Fiber Connector Utilizing Elastomeric Alignment Device" for single and plural transmission lines. The ends of the individual fibers are brought into alignment by being passed through cylindrical guides biased by a surrounding elastomeric alignment element. U.S. Pat. No. 4,214,810--Stewart discloses a "Method of Connecting Optical Fibers" in which, as best shown in FIG. 5 thereof, two parallel transmission lines each terminate in one holder so that when the holders are brought together using alignment pins, the ends of the fibers are properly aligned. U.S. Pat. No. 4,215,913--Turley et al discloses "Optical Fibre Connectors" for a single transmission line having self-centering guide means for causing alignment of the ends of the transmission line.